Diisopropylamide, lithium salt

Very high levels of induced diastereoselectivity are also achieved in the reaction of aldehydes with the titanium enolate of (5)-l-rerr-butyldimethylsiloxy-1-cyclohexyl-2-butanone47. This chiral ketone reagent is deprotonated with lithium diisopropylamide, transmetalated by the addition of triisopropyloxytitunium chloride, and finally added to an aldehyde. High diastereoselectivities are obtained when excess of the titanium reagent (> 2 mol equiv) is used which prevents interference by the lithium salt formed in the transmetalation procedure. Under carefully optimized conditions, diastereomeric ratios of the adducts range from 70 1 to >100 1. 

Lithium salts of resonance-stabilized organic anions have also found a role in carbon-phosphorus bond formation by displacement at phosphorus. The generation of the lithium salt derived from acetonitrile (or other aliphatic nitriles by reaction with butyl lithium or lithium diisopropylamide) provides for carbon-phosphorus bond formation by displacement of halide from phosphorus (Equation 4.24).68... 

The lithium salts of the a-sulfinyl carbanions have been alkylated by alkylating reagents other than iodomethane. For example, alkylation of ( + )-l-[( )-ethylsulfinyl]-4-methylbenzene with lithium bromoacetate in the presence of lithium diisopropylamide gave (5)-3-[(2 )-4-methylphen-ylsulfinyl]butanoic (7) acid as the major product (d.r. 8 2) which was isolated as a pure solid in 58% yield55. 

Lithium diisopropylamide- Diisopropylamine, lithium salt (8) 2-Propanamine, N-(l-methylethyl)-, lithium salt (9) (4111-54-0) Lithium, methyl- (8,9) (917-54-4)... 

Camphor (8) Bicyclor2.2.11heptan-2-one, 1,7,7-tr1methyl- (9) (76-22-2) Lithium diisopropylamide Diisopropyl amine, lithium salt (8) ... 

Addition of r-butyl acetate to lithium diisopropylamide (LDA) in hexane at - 78°C gives the lithium salt of r-butyl acetate456 (2-22) as a stable solid. The nmr and ir spectra of this... 

The reactions of 57a with LiPPh2 and lithium diisopropylamide were sluggish in THF, 58 being the main product. No reaction was observed with the lithium salt of 2-nitro-propane nor with lithium /-propanethiolate134. 

Sometimes this equilibrium mixture of enolate and base won t work, usually because the base (hydroxide or alkoxide) reacts with the electrophile faster than the enolate does. In these cases, we need a base that reacts completely to convert the carbonyl compound to its enolate before adding the electrophile. Although sodium hydroxide and alkoxides are not sufficiently basic, powerful bases are available to convert a carbonyl compound completely to its enolate. The most effective and useful base for this purpose is lithium diisopropylamide (LDA), the lithium salt of diisopropylamine. LDA is made by using an alkyllithium reagent to deprotonate diisopropylamine. 

In a nice illustration of the impact of metal coordination upon the reactivity of phospholes, a methodology for the functionalization of these heterocycles in the /3-position has been described (see also Scheme 22) <2001JOM105>. Here, coordination of both the P-lone pair and the cyclic diene system was undertaken. The resulting multimetallic complex 79 was treated with lithium diisopropylamide (LDA) to afford the lithium salt 350 (Scheme 118). This readily undergoes nucleophilic substitution with a variety of electrophiles to afford the corresponding substituted phosphole complexes 351-353. The free phospholes can be isolated following decomplexation with cerium(iv) ammonium nitrate (CAN). 

The most versatile method of preparing a-azidocarboximides2 and protected a-amino acids is based on early investigations3. In this study the lithium enolate 2 of the azetidinone 1 [prepared with lithium diisopropylamide (LDA)] is treated with tosyl azide to afford an adduct 3, isolated and characterized by IR spectroscopy as the lithium salt of an acyclic triazene3. 

P-Hydroxy acidsf a-Lithiatcd lithium salts of aliphatic carboxylic acids can be prepared by the reaction of the carboxylic acid with lithium diisopropylamide (.3, 184). These react with aldehydes and ketones to give fair to good yields of j7-hydroxy acids (the method is an alternative to the classical Rcformalsky reaction). Both mono- and... 

The lithium salt of methyl 2,4-dimethoxy-6-methylpyrimidine-5-carboxylate, generated by deprotonation with lithium diisopropylamide in diethyl ether at 70 °C, reacts smoothly as a... 

Apart from the bases mentioned a series of other nitrogen bases (ammonia, triethylamine, pyridine, cyclic amidines, lithium diethylamide, lithium diisopropylamide, lithium piperidide, etc.) have been used to deprotonate phosphonium salts. 

In practice, the strong base lithium diisopropylamide [LiN(i-C3H7)2 abbreviated LDA] is commonly used for making enolate ions. As the lithium salt of the weak acid diisopropylamine, pl a = 36, LDA can readily deprotonate most carbonyl compounds. It is easily prepared by reaction of butyllithium with diisopropylamine and is soluble in organic solvents because of its two alkyl groups. 

Common reagents such as lithium diisopropylamide (LDA see Chapter 11, Problem 5) react with carbonyl compounds to yield lithium enolate salts and diisopropylamine, e.g., for reaction with cyclohexanone. 

A stronger base and notably weaker nucleophile is the anion of hexamethyl-disilazane (Mc3Si)2NH, (34H). The anion, (34) , is electrogenerated ex situ, similarly to (33) , as its magnesium salt in dimethoxyethane with 15% v/v HMPA [75]. The PB (34H) is commercially available, relatively cheap, and in many respects behaves very much Kke lithium diisopropylamide (LDA). Substitution of HMPA with Ai-methyl-2-pyrrolidone was not successful [75]. 

Triethylamine in THF can be used as the external base to deprotonate triazolium salts. The resulting NHCs were complexed in situ, e.g., to [(/7 -cymene)RuCl2]2, [(/ -cod)RhCl]2, and [(/ -C5Me5)RhCl2]2. Sodium carbonate in water/ DMSO deprotonates imidazolium iodides in the presence of mercury(II) dichloride to give [Hg(NHC)2][Hgl3Cl]. " A pyridine-functionalized imidazolium salt was deprotonated by lithium diisopropylamide (LDA) in THF and attached in situ to [(p -cod)Pd(Me)Br] [Eq.(17)]. After abstraction of the bromide anion with silver(I) a tetranuclear ring is formed. 

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